Numbering Resources

Central Office Codes

Central office codes, also known as exchanges, prefixes, or simply NXXs, are digits 4, 5 and 6 of a ten-digit geographic NANP telephone number. NANPA assigns central office codes to state-authorized local service providers using industry-developed guidelines and federal directives. Because the application and qualification process is complex, potential applicants should read and understand the guidelines.

Special rules apply in area codes that are in "jeopardy," that is, in danger of running out of numbers before relief can be provided. In these areas, industry-developed jeopardy procedures specify important overrides to the central office code assignment process.

Entering Rating and Routing Information

Once NANPA has confirmed an assignment by returning a Confirmation of Assignment, known as a Part 3 form, to the applicant, the applicant must arrange for the entry of Part 2 rating and routing data.

Expediting Central Office Code Assignment In-Service Dates

The process of getting a newly assigned central office code in service is lengthy; but, under certain circumstances described in the guidelines, the interval can be shortened. This is commonly referred to as a code expedite. This can be done only with the concurrence of the interconnecting tandem owner.

NANPA must begin reclamation procedures if an assignee fails to return a Part 4 form within six months after the original effective date returned to the applicant on the Part 3 form and entered into the ACD screen in the BIRRDS database. The ultimate decision whether to reclaim a code or grant an extension is made by designated state or federal regulatory authorities. Service providers may designate individuals to serve as contacts for reclamation activities affecting their companies.

Changing Assignment Information

Central office code assignees should be aware that the guidelines require them to submit a change request to NANPA via a Part 1 CO Code (NXX) Assignment Request Form. This includes changes such as, but not limited to, the tandem homing arrangement, OCN, switching entity/POI and rate center (including a rate center consolidation). For OCN changes due to merger/acquisition, the SP must so state on the Part 1 form. Use the NANP Administration System for this purpose.

Returning central office codes that contain ported numbers can disrupt customers with these ported numbers. The industry has developed a process to insure that disruption does not occur. Central office code assignees intending to return codes containing ported numbers must follow this process. The process requires all central office code assignees to monitor the pending disconnects report (xls) to check for codes in which they have customers as a result of porting. Additional information on this topic may be found in Appendix C of the central office code assignment guidelines.